A compressor generally of the sliding vane type comprises, as shown in FIG. 1, a cylinder 51 having an interior cylindrical space, side plates (not shown in FIG. 1) which are fixed to opposite side faces of the cylinder and tightly closing side faces of a vane chamber 52 as the interior space of the cylinder, a rotor 53 which is arranged eccentrically within the cylinder 51, and plural vanes 55 engaged slidably in respective grooves 54 provided on the rotor 53. A suction port 56 is formed on a side plate, and a discharge hole 57 is formed in cylinder 1. Vanes 55 are urged outwardly by centrifugal force upon rotation of the rotor 53, such that the tip end face of each vane slides on the interior wall face, thereby to prevent leakage of gas from the compressor.
In such a sliding vane type rotary compressor a small and simple construction is possible, compared with the reciprocating type of compressor which is complex in construction and has a large number of parts, and thus recently has been employed as a car air conditioner compressor. However, in this rotary type compressor, there are the following problems compared with the reciprocating type compressor.
Namely, in the case of an automobile air conditioner cooler, the driving force of the engine is transmitted to a pulley of a clutch through a belt and drives a rotary shaft of the compressor. Accordingly, when the sliding vane type compressor is used, its refrigerating ability increases in a straight line in proportion to the rotational speed of the engine of the vehicle.
On the other hand, when the reciprocating type compressor is used, the follow-up property of the suction valve becomes poor at the high speed rotation range, and compressed gas cannot be sucked fully into the cylinder. As a result, the refrigerating ability is saturated at the high speed range. That is, in the reciprocating type compressor, a restraining action on the refrigerating ability acts automatically at the high speed traveling range, while in the rotary type compressor there is no such action, and refrigerating efficiency is decreased due to an increase in compression, or an over-cooled state. As a means to avoid this problem with a rotary compressor, it has been proposed to provide a control valve to vary the opening area of a passage communicated with suction port 56 of the rotary compressor, whereby control is achieved by throttling the opening area at the high speed rotation range. However, this solution has the problems that the control valve must be added separately, and the construction thereof is complex and the cost thereof is high.
As another means to avoid over cooling of the rotary compressor at the high speed range, there has been proposed a construction in which the rotational speed is not increased over a certain value by using fluid clutch, planetary gear, etc. However, in the former, energy loss due to frictional heat generated between relative moving faces is large, and in the latter, the dimensions and shape are large by adding a planetary gear mechanism having a large number of parts. Thus, both these solutions are difficult to utilize practically in recent years when simplification and compactness are required increasingly by the trend for energy savings.